P-015 - Exploring the potential of diffusible signal factor (DSF) as an adjuvant in antimicrobial strategies for Huanglongbing (HLB) control

Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas) and transmitted by Diaphorina citri, is the most devastating disease affecting sweet orange production worldwide. The diffusible signal factor (DSF), a quorum-sensing (QS) molecule involved in microbial communication, has shown potential for controlling bacteria by modulating virulence and increasing susceptibility to antimicrobials. In this context, the objective of this study was to evaluate whether a DSF molecule (12-methyltetradecanoic acid), alone or combined with antimicrobials, inhibits Liberibacter crescens, a culturable CLas surrogate. The effect of DSF (50–250 µM) on L. crescens growth was assessed via optical density measurements over five days. The same approach was used to evaluate DSF synergy with gentamicin, streptomycin, and kanamycin. Gentamicin was chosen for its known synergy with DSF against human pathogens, while kanamycin and streptomycin are effective against HLB. Higher DSF concentrations (200–250 µM) reduced bacterial growth from 48 hours, while lower concentrations (50–100 µM) had a significant effect from 72 hours. Additionally, 50 µM of DSF enhanced bacterial susceptibility to gentamicin (2–8 µg/mL), kanamycin, and streptomycin (1.56–12.5 µg/mL), reducing their minimum inhibitory concentration (MIC). These findings highlight DSF’s potential as an adjuvant to boost antibiotic efficacy against HLB. Ongoing studies are exploring its synergy with other antibiotics and antimicrobial compounds from the citrus microbiome to develop integrated control strategies.